The imparting of a decorative appearance to surfaces of furniture or floors and the reduction of their sensitivity to mechanical, thermal and chemical stress through application of laminates is known. Here, for example the reduction of sensitivity to scratches and stains may be mentioned. The laminate should moreover be as transparent as possible.
Laminates often consist of one or several paper layers which are impregnated with a thermally curing synthetic resin. Also, hard substances are often incorporated in the top paper layer in an attempt to further increase the scratch and abrasion resistance of laminates. For this, aluminium oxide has proved to be a particularly suitable hard substance.
In WO 01/53387, the production of curable coatings with a macroscopic texture, starting from a coating mixture which contains an irradiation curing resin, an initiator and a rheology adjuster, such as for example nanoscale aluminium oxide particles, is disclosed. For this, the aluminium oxide particles are incorporated into the coating mixture in the form of a powder at a concentration of 1 to 40 wt. %. Further, a coupling agent can be added to the coating mixture, for the purpose of improving the distribution of the aluminium oxide particles in the coating mixture and ensuring good bonding in the cured coating. Homogeneous distribution of the particles in the coating mixture is a problem when this contains high concentrations of particles. However, for high mechanical stability of the cured coating, as high a concentration of aluminium oxide particles as possible is desirable. Furthermore, the viscosity rises with the concentration of the aluminium oxide particles in the coating mixture. In WO 01/53387, aluminium oxide concentrations up to 40 wt. % in the coating mixture are admittedly disclosed, however, at such high concentrations, the coating mixture is now almost impossible to process.
EP-A-1252239 discloses the use of powders and dispersions of aluminium oxide for the production of laminates. A disadvantage in the aluminium oxide products disclosed is the low content thereof, for example 15 wt. % in Example 2, in melamine-containing preparations and hence in the laminate, as a result of which the mechanical properties of the laminate can only be improved to an inadequate extent. A further disadvantage is that, with the requirement for high transparency, water-based dispersions yield less good results than dispersions based on an organic solvent. However, high solvent concentrations are not desirable for environmental compatibility and plant safety reasons.